A hierarchical approach to the study of the exponential failure model

The exponential failure model is studied from the hierarchical point of view. The parameter of the exponential is considered as a random variable with a gamma function as a prior. Futhermore, the scale parameter of the gamma prior isassumed to be a random variable with known hyperprior. Under these assumptions estimators are derived for the exponential parameter and reliability function. Monte Carlo simulation is utilized to compare the various estimators.     

MRP system performance under lumpy demand environments

Material requirements planning (MRP) systems are deemed to deal with master schedules with lumpy demand patterns better than any other production scheduling system. Past studies have advocated important advantages of using MRP systems. The objective of this paper is to look into the impact of patterns of demand lumpiness on the performance of MRP systems by a simulation study. Results show that there is an important threshold point in terms of degree of lumpiness at which MRP system performance starts to deteriorate in the operating conditions considered. If master production schedules (MPS) can be controlled by manufacturers, MRP users should exercise caution to introduce demand lumpiness in MPS to improve system performance. If not, MRP users should then examine the given lumpiness and choose an appropriate lot-sizing rule that has been shown to take advantage of the effect of demand lumpiness.     

Generalizations of Mathisen's median test for comparing several treatments with a control

A distribution-free test for comparing several treatments with a control is proposed for one-way classified data. It is advantageous to use the test in life-testing experiments where testing time is expensive. The proposed test has a shorter expected duration than a previously proposed test by Slivka(1970). The optimal allocation of the experimental units to the treatments for two situations are given. In a simulation study the power of the test is compared with the power of Slivka's test. An extension of the test for two-way classified data is given     

Real-time operation selection in an FMS using simulation- a fuzzy approach

Production management and scheduling problems in flexible manufacturing systems (FMSs) are more complicated than those problems in job shops and transfer lines. Due to the flexibility of FMSs, alternative operation is common. When considering the operational problems of FMSs such as scheduling, simulation methodology seems to be useful to address these issues. Real-time scheduling schemes use simulation techniques     

A comparison of species diversity estimators

Although having been much criticized, diversity indices are still widely used in animal and plant ecology to evaluate, survey, and conserve ecosystems. It is possible to quantify biodiversity by using estimators for which statistical characteristics and performance are, as yet, poorly defined. In the present study, four of the most frequently used diversity indices were compared: the Shannon index, the Simpson index, the Camargo eveness index, and the Pielou regularity index. Comparisons were performed by simulating the Zipf–Mandelbrot parametric model and estimating three statistics of these indices, i.e., the relative bias, the coefficient of variation, and the relative root-mean-squared error. Analysis of variance was used to determine which of the factors contributed most to the observed variation in the four diversity estimators: abundance distribution model or sample size. The results have revealed that the Camargo eveness index tends to demonstrate a high bias and a large relative root-mean-squared error whereas the Simpson index is least biased and the Shannon index shows a smaller relative root-mean-squared error, regardless of the abundance distribution model used and even when sample size is small. Shannon and Pielou estimators are sensitive to changes in species abundance pattern and present a nonnegligible bias for small sample sizes (<1000 individuals). Received: May 8, 1998 / Accepted: May 6, 1999     

Prevalence of low testosterone in aging men with benign prostatic hyperplasia: data from the Proscar Long-term Efficacy and Safety Study (PLESS)

Abstract

Objectives: We examined the prevalence of low testosterone (LT) in the subset of men in the Proscar Long-term Efficacy and Safety Study (PLESS) who had serum total testosterone (TT) measured at baseline.

Methods: PLESS enrolled 3040 men with benign prostatic hyperplasia (BPH). Of these men, 299 had TT and body mass index (BMI) measurements at baseline. Patients were classified as having LT if their baseline TT was <300?ng/dl.

Results: Of the 299 PLESS patients with baseline TT and BMI measurements, 65 (21.7%) had LT. The prevalence of LT increased with increasing BMI, occurring in 8/78 (10.3%) normal weight patients (baseline BMI <25?kg/m²), 35/160 (21.9%) overweight patients (baseline BMI ≥25–<30?kg/m²), and 22/61 (36.1%) obese patients (baseline BMI ≥30?kg/m²).

Conclusions: LT was observed in more than one in five PLESS patients with baseline TT and BMI measurements. The prevalence of LT increased with increasing BMI – more than one in three obese PLESS patients with baseline TT measurements had LT.     

本期视点:多重主客统一视野中的《春秋》学研究

董仲舒的<春秋>学认为:第一,<春秋>称国君即位之年为"元年","元"乃更始,有断与续相统一的寓意.第二,<春秋>书"王正月",是为了"大一统",王者改制必然导致"统"的更迭,"通三统"是一个循环,叫做"三而复";此外,还有"再而复"、"四而复"、"五而复"、"九而复".历史的无穷演进恰是由多重的"复"构成的,表现了复与往的统一.第三,<春秋>把鲁国十二公划分成三个阶段,各自的"书法"不同,内与外、夏与夷的界限逐渐消弭,有以横向的社会交往说明纵向的历史发展之意,表现了横与纵的统一.第四,<春秋>有"常义"有"应变"."常义"固须遵从,"应变"更为重要,因为它更贴近不断发展着的仁爱之道;历史正是在"常义"的突破中不断前进的;这是常与变在历史的深层结构中的统一.这些观点有"通古今之变"的意义,属于通史精神的范畴.     

Efficient jobshop dispatching rules: Further developments

Many dispatching rules for scheduling in dynamic jobshops have been proposed over many years. The research issues in jobshop scheduling seem to be still open in the sense that no single rule has been found to be the best under all shopfloor conditions even with respect to one single measure of performance. Added to this problem, there are several measures of performance, e.g. the minimizations of mean, maximum and variance of flowtime, percentage of tardy jobs, and mean, maximum and variance of tardiness of jobs. Recent studies have reported the development of more efficient dispatching rules than the popular rules, e.g. SPT, COVERT, MOD and ATC. This study is an attempt to improve some of the recently reported dispatching rules. An extensive simulation study reveals that the improved rules developed in the present study appear to be quite effective in minimizing mean flowtime, and maximum tardiness and variance of tardiness of jobs.     

《史记》研究三君子——美国汉学家华兹生、候格睿、杜润德《史记》研究著作简论

华兹生、候格睿、杜润德是美国汉学界史记学研究领域最负盛名的学者。他们分别撰写的三部史记研究论著堪称该领域奠基之作,具有十分重要的学术价值,然而国内学术界目前鲜有文章论述这些著作。本文将对这三部著作进行一番介绍和评述,以唤起国内史记研究专家对此的关注。     

行政管理学教学研究中的问题

行政管理学的教学研究只有与中国行政管理的实践相结合、与中国社会发展对行政管理学的要求相结合,才会有旺盛的生命力。目前行政管理学教学研究中存在着“三多三少”:讲外国的多,讲中国的少;讲理论的多,讲应用的少;讲过去的多,讲现在的少。为此,在行政管理学教学研究中要努力做到:本土化、时代性、实践性、开放性。